Apparatus for the production of electrically heated window

ABSTRACT

A laminated safety glass window is described having a clear polymer inner layer which includes a pattern of wrinkled resistance wires oriented in non-parallel random fashion so as to reduce glare from the wires when the window is used as a windshield. The individual resistance wires are partially embedded in the polymer sheet by a technique utilizing shrinkage of a thermoplastic polymer from its original dimensions when heated to an elevated temperature together with having the individual wires change configuration when relaxed from tension forces on the wire when first assembled with the polymer sheet. A method of forming the wire-incorporated polymer sheet member is also described along with equipment for automatically applying prestressed resistance wire to a thermoplastic sheet followed by heating the assembly under proper conditions to form the composite member.

Elited States Patent [1 1 Gruss et al.

[4 1 Mar. 5, 1974 APPARATUS FOR THE PRODUCTION OF ELECTRICALLY HEATEDWINDOW [73] Assignee: General Electric Company,

Schenectady, NY.

[22] Filed: Dec. 27, 1972 [21] Appl. No.: 3l8,867

Related US. Application Data [62] Division of Ser. No. 166,064, July 26,1971, Pat. No.

[52] US. Cl 425/517, 264/249, 425/90, 425/111, 425/112, 425/403, 425/502[51] Int. Cl. B29c 27/14 [58] Field of Search... 425/109, 403, 393, 501,502, 425/517, 90, 111, 112; 264/249, 230, 272; 219/522, 544; 338/268[56] 9 References Cited 'UNITED STATES PATENTS 1,009,002 11/1911 Welch425/393 1,643,998 10/1927 SCOIL; 264/249 X 3,436,041 4/1969 Haller264/249 X 3,475,595 10/1969 Leclercgm. 219/522 3,526,692 9/1970 Onako425/119 X 3,541,682 1l/l970 Hildebrandt.. 264/249 X 3,728,425 4/1973Schradcr.....= 260/230X Primary Examiner-Robert L. Spicer, Jr. Attorney,Agent, or Firm-John F. McDevitt; Henry P. Truesdell; Frank L. Neuh'auser[5 7 ABSTRACT A laminated safety glass window is described having aclear polymer inner layer which includes a pattern of wrinkledresistance wires oriented in non-parallel random fashion so as to reduceglare from the wires when the window is used as a windshield. Theindividual resistance wires are partially embedded in the polymer sheetby a technique utilizing shrinkage of a thermoplastic polymer from itsoriginal dimensions when heated to an elevated temperature together withhaving the individual wires change configuration when relaxed fromtension forces on the wire when first assembled with the polymer sheet.A method of forming the wire-incorporated polymer sheet member is alsodescribed along with equipment for automatically applying prestressedresistance wire to a thermoplastic sheet followed by heating theassembly under proper conditions to form the. composite member.

2 Claims, 6 Drawing Figures PATENTED 5 74 APPARATUS FOR THE PRODUCTIONOF ELECTRICALLY HEATED WINDOW This application is a division of ourearlier applicai n. er- NQ- 63.0 fi s Ju y 1. 7. .1 ndn i sued us. Pat.No. 3,7 29,616.

BACKGROUND OF THE INVENTION tance wires that is substantially free fromglare when two glass sheets and bus-bar terminals are affixed at eachend of the individual wires to form the electrical heating circuit. In asecond method of making the elec- I trically heated window glass, apattern of straight wires are aligned in closely spaced parallelrelationship then applied to a glass plate. Another glass plate isapplied thereto to form the sandwich construction and the assembly isthen heated to provide the integral product. To achieve the desiredparallel wire orientation in this second method, the individual wiresare secured under tension in a skeleton frame which keeps the individualwires straight until bonded in the final sandwich assembly. Still athird method for incorporating electrical heating wires into a laminatedsafety glass construction applies a wire pattern made up of a pluralityof closely spaced parallel extending wires upon a clear thermoplasticsheet and tacks the ends of the individual wires with a metal strip ateach end. The composite inner layer isthen laminated in a conventionalmanner to provide the final safety glass window. the parallel orientedpattern of resistance Wires in this third method are thermally tackedalong their length to the sheet before the final lamination step topreclude relative movement between the wires.

In all of the above methods it has been found that glare is producedfrom a parallel orientation of resistance wires in the glass sandwich.More particularly, there is glare due to either optical reflection oroptical diffraction of light rays from the individual wires which istransmitted to the eyes of a viewer looking through the glass sandwich.The glare is especially noticeable under strong lighting conditions suchas bright daylight or the headlights of an oncoming vehicle which couldpreclude acceptance of the final product for vehicle windshieldapplications.

SUMMARY OF THE INVENTION Applicants have discovered a novel techniquefor incorporating electrical resistance wire in a thermoplastic polymersheet to provide an essentially glare-free pattern when observingobjects through the window. The improved construction forms the innerlayer of a laminated safety glass member which can be used as a vehiclewindshield with the ability to remove ice and snow as well as defrost.

The object of the present invention, therefore, is to provide a superiorelectrically heated safety glass construction along with methods andapparatus to form such a member. Still a further object is to provide anelectrically heated windshield with improved thermal capacity fordefrosting as well as removing ice and snow from the windshield. Stillanother object of the present invention is to provide simple andreliable means of assembling resistance wires with a thermoplasticpolymer sheet so that the composite assembly can be easily handledthereafter to produce a laminated safety glass member by conventionaltechniques.

Briefly stated, the invention in certain of its embodiments provides acomposite member comprising a layer of transparent thermoplastic polymerwhich shrinks from its original dimensions when heated to an elevatedtemperature having partially embedded in one major surface a pluralityof wrinkled resistance wires which lie in closely spaced relationshipand are oriented with respect to one another in non-parallel randomfashion both in the plane of said major surface as well as in a plane atsome angle thereto so as to reduce glare when light is transmittedthrough the composite member. The term transparent as used herein torefer to a thermoplastic polymer material includes material havinglimited optical clarity but permitting visual identification of objectsviewed from the opposite side of the polymer sheet.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of acurved window member having a laminated safety glass constructionaccording to the present invention;

FIG. 2 is a vertical section through the windshield member of FIG. 1;

FIG. 3 is a top view partially in cross section of a compositethermoplastic sheet incorporating the random wire pattern produced inaccordance with the invention;

FIG. 4 is a sectional view ofa segment of the composite member depictedin FIG. 3 wherein one bus-bar electrode is electrically connected to theresistance wire pattern;

FIG. 5 is a perspective view of equipment used to assemble a compositethermoplastic sheet member having the resistance wire pattern of thepresent invention; and

FIG. 6 is a cross-sectional view of a collapsible drum utilized in theFIG. 4 equipment with the composite thermoplastic sheet member woundabout its periphery.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention providessimple and effective means to reduce a major difficulty encountered witha parallel arrangement of resistance heating wires in a laminated safetyglass member. While the glare phenomena encountered is not fullyunderstood at the presenttime, it is believed attributable to the wiredi-. rection rather than spacing between the wires. By ran- 4 domizingthe wire direction in accordance with practice of the present invention,it becomes possible to distribute light refiection or diffraction fromthe individual wires in all directions and thereby reduce or eliminatethe glare. While a complete randomization of the individual wires wouldbe most diff cult to achieve, the applicants have found that acontrolled randomization is sufficient to substantially eliminate theglare problem.

Controlled randomization of the resistance wire pattern is obtained byapplying prestressed resistance wires upon one major surface of thesheet of transparent thermoplastic material and thereafter utilizing anability of the polymer material to shrink from its original dimensionswhen heated to an elevated temperature to embed portions of theindividual wires in the contacted surface of thermoplastic material.More particularly, a pattern of the prestressed resistance wires isapplied under tension to one major surface of the thermoplastic sheet sothat individual wires are in closely spaced parallel relationship andthe composite member so formed is then heated under conditions whichpermit the individual resistance wires to expand and adopt aconfiguration attributable to the prestressed forces while becomingpartially embedded in the softened thermoplastic material. Subsequentcooling of the composite member provides the final ran-.

domization in the wire pattern such that individual wires have awrinkled or irregular crimp at irregular intervals along their length toprovide the non-parallel relationship between adjacent wires. The finalnonparallel wire pattern will be governed by thermal expansiondifferences between the polymer and the wire, the nature and extent ofprestress forces applied to the resistance wire before incorporation inthe polymer surface, and the heat shrinkage characteristics of thethermoplastic material. Said non-parallel random configuration of thewire exists both in the plane of a major surface of the polymer sheet aswell as ina plane at some angle thereto.

The relatively high heating capacity of the wire pattern obtained bypractice of the invention is due to using fine wire having a diameterfrom approximately 0.0003 inches to 0.0009 inches in a spacing from to30 wires/inch. While it is recognized that wattage dissipation obtainedby connecting the wire pattern to a source of electrical energy willdepend upon such factors as voltage and contact resistance as well asdiameter of the wire and spacing of wires, it has been reported that awire pattern as above described can provide from 0.25 watts/inch squareto 0.5 watts/inch square wattage dissipation when connected to aconventional automotive power supply which is said to be adequateheating energy to defrost a windshield quickly over a much larger areathan is possible with conventional hot air defrosting. The heatingcircuit can be provided with copper strip bus-bars of A inch width and a0.002 inch thickness being applied at each end of the individualresistance wires to provide a parallel electrical connection which isnot affected by short circuit ifthe individual wires become crossedduring fabrication of the random wire pattern. Minimum contactresistance can be obtained at the bus-bar connections by laying thecopper strips across the wire and thereafter assembling the final windowconstructon which can be heated to approximately 275F under about 300psi. pressure to laminate the entire assembly. Understandably, otherelectrode means than bus-bars are contemplated within the scope of thepresent invention as well as different electrically conducting materialsthan copper for said electrodes.

Turning now to the drawings, FIG. 1 represents a schematic view of aconventional automobile windshield having the substantially glare-freeresistance wire pattern produced in accordance with the invention. Moreparticularly, a laminated safety glass sandwich 10 is shown whichcomprises apair of outer glass layers 12 and 14 which are held togetherby adhesive bonding to composite thermoplastic sheet member 16 as anintegral construction. Said composite thermoplastic inner layer 16(which isshown more clearly in FIG. 2) includes a sheet of transparentthermoplastic polymer 18 having partially embedded in one major surfacea plurality of wrinkled resistance wires 20 which are oriented withrespect to one another in nonparallel random fashion. Bus-bar strips 22and 24 are disposed at each end of the individual resistance wires toprovide electrode means for heating the wires from the already availableelectrical power supply in the vehicle.

In FIG. 2 there is shown a vertical section through the windshieldmember of FIG. 1 which more clearly illustrates a greater degree ofrandomness assumed by the individual resistance wires 20 in the finalwindshield assembly. More particularly, when said resistance wires arefirst incorporated in composite sheet member 16 to provide an innerlayer for bonding the outer glass layers together, there is athree-dimensional wire configuration wherein the wires are oriented withrespect to one another in non-parallel random fashion both in the planeof a major surface of the polymer sheet as well as in a plane at someangle thereto which can be seen in greater detail by reference to FIGS.3 and 4. Those portions of the individual wires which protrude from thepolymer surface 26 are free to move when compressed by the adjacentglass layer 14 during lamination of the final glass sandwich. In sodoing, the wires undergo further random orientation with respect to theplane of said major surface in said final assembly. Said in another way,the composite thermoplastic sheet member 16 produced in accordance withthe invention is so formed to enhance random orientation of theindividual resistance wires when assembled in the final glass sandwichconstruction.

FIG. 3 is a top view partially in cross section of the compositethermoplastic member 16 which is produced in a manner to be more fullyexplained hereinafter. Thermoplastic sheet element 18 comprises atransparent thermoplastic polymer which shrinks from its originaldimensions when heated to an elevated temperature having partiallyembedded in major surface 26 a plurality of wrinkled resistance wiresillustrated by numerals 28, 30 and 32 which protrude from said majorsurface in random fashion where not embedded in the polymer material. Itcan also be noticed that said individual wires are further oriented withrespect to one another in random fashion and lie in closely spacedrelationship to provide the wattage dissipation needed for defrosting aswell as ice and snow removal.

FIG. 4' is a sectional elevation view of a segment 'of the compositemember depicted in FIG. 3 which includes one bus-bar electrode 22 notshown in the preceding figure. It can be noted that the bus-barelectrode lies intermediate the wire pattern and the polymer sheetalthough it is within contemplation of the present invention to providedifferent orientation of the electrode means in the composite sheetmember. The busbar strips can be affixed to the individual resistancewires and the underlying thermoplastic sheet 18 to provide minimalcontact resistance during the thermal tacking step used to assemble thecomposite member. It can also be noted in FIG. 4 that portions of theindividual resistance wire shown protrude at different elevations fromthe surface of the polymer sheet due to localized differences governingdistribution of said wire with respect to the polymer sheet.

FIG. 5 is a perspective view of equipment which can be used to assemblethe composite member 16. A modified machine lathe 34 provides thesupport means for rotatably mounting a collapsible drum member 36 uponwhich the polymer sheet and wire constituents of the composite memberare wound. More particularly, headstock 38 and tailstock 40 provideconvenient means to suspend the drum member therebetween for subsequentwinding and heating of the composite assembly. Collapsible drum member36 has an exterior cylindrical shell 42 which includes a slot 44extending along its entire axial length to permit decreasing the drumcircumference by a predetermined amount after initial assembly of thecomposite sheet member and prior to a heat shrinkage procesing step. Theslot opening in said drum member is occupied by overlapping panel 46 toprovide a continuous surface on the drum for winding the polymer sheetand the wire pattern. The drum construction is depicted more clearly inFIG. 6 along with the wrapped composite sheet member. The drum member 36further includes a feed screw assembly 48 affixed to the interior wallof shell 42 which cooperates in reducing the drum circumference. Thefeed screw assembly includes a feed screw 50 aligned along thelongitudinal axis of the drum which threadably engages web member 52 topermit radial displacement of arms 54, 56 and 58 by conventional linkagenot shown. A duplicate web member at the opposite end of the drum member(which is also not shown) engages the feed screw in like manner toprovide a means of uniformly reducing the drum diameter along its entirelength. An unthreaded portion 60 is provided on the feed screw toprovide convenient gripping means for operating the feed screw assemblyto adjust the drum diameter.

Lathe 34 includes a carrier assembly 62 which can be mounted upon thetool guide means ordinarily employed with a machine lathe to providemovement of the supported structure in a direction parallel to thelongitudinal axis of the lathe. The carrier assembly includes a spool 64of the resistance wire 28 rotatably mounted in frame 66 as a means ofsupplying the wire for winding around the drum periphery. Said carrierassembly also includes guide means 68 which positions the wire beingsupplied in the mesh between spur gear members 70 and 72 prior towinding about the drum periphery. Said spur gears are rotatably mountedupon the carriage assembly in a loosely meshing engagement sufficient topermit passage of the thin resistance wire being employed withoutbreakage while applying a slight crimp to the wire being processed. Moreparticularly, said gear means provide a prestress condition to the wireprior to its assembly with the thermoplastic sheet on the drum peripherysuch that said wire can thereafter be applied under tension as straightwire which becomes crimped or wrinkled only upon removal of the tensionforces after winding in a manner to be described.

Lathe 34 is also equipped with a pair of electrical power supply members74 and 76 that are connected to bus-bar strips 78 and 80, respectively,to provide means for heating the composite member after assembly. Itshould be appreciated that while separate and distinct bus-bar stripsare employed in fabricating the composite member from the bus-bar strips22 and 24 employed in the final laminated safety glass sandwich to heatthe window that it is within contemplation of the present invention toemploy a single pair of bus-bar strips for both purposes.

In operation, a sheet of thermoplastic material 18 is wound about thedrum periphery and secured to said periphery at each end with adhesivestrips 82 and 84 at a location which can correspond to placement of thebus-bars. Bus-bar strips 78 and are next affixed to the externalperiphery of the drum member by additional adhesive strips 86-90 locatedat each end of the bus-bar elements. Next, a helical coil of theprestressed resistance wire 28 is wrapped about the drum periphery inclosely spaced relationship by activating the carriage assembly whilethe drum is being rotated all in conventional lathe operation technique.The wire pattern being applied to one major surface of the polymer sheetconforms to a parallel orientation between adjacent wire turns and thehelical wire coil is then secured to the drum periphery with additionaladhesive strips (not shown) which can be disposed at the same locationbeing occupied by the bus-bars. The wire coil can then be cut along itslength in the spacing between said busbars to define an electrical pathentirely about the circumference of the coil for heating the assembly toprovide the composite sheet member.

After assembly of the composite member in the manner above indicated,the wire pattern is embedded in the plastic sheet by heating thecomposite member under conditions permitting the resistance wire toadopt a configuration attributable to the prestress forces whilemaintaining the polymer sheet in physical contact with the resistancewire on the drum periphery. Specifically, the drum circumference isreduced sufficiently to permit the composite member to sag undergravitational forces from the drum surface which relaxes the tensionforces on the resistance wire enabling it to crimp or wrinkle along itslength while still maintaining point contact with the polymer sheet.Electrical energy is supplied to the wire pattern while in this saggedconfiguration which heats the polymer material to its softening pointthereby permitting portions of the wire still in physical contact withthe polymer surface to become embedded therein. Under such heatingconditions, both polymer sheet and wire pattern are permitted to expandand contract along the direction of the wire path depending uponindividual thermal expansion characteristics while still remaining inphysical contact. It has been noted during this heating operation thatthe polymer sheet contracts visibly while still being heated after firstundergoing thermal expansion with the shrinkage occurring along thedirection of the wire path. Heating is discontinued by interrupting theelectrical energy being supplied to the wire pattern after the shrinkagehas taken place whereupon the composite member is allowed to cool whichproduces an adhesive bond with the wire pattern. By reason of alignmentbetween the wire path and the shrinkage direction in the polymer sheet,it can be seen that a greater randomization in the final wire pattern isprovided than otherwise would occur. It has also been noted duringexperience with this process that certain polyvinyl butyral polymersheets which are conventionally employed as the inner layer in laminatedsafety glass undergo greater shrinkage in one direction along the majorsurface than in a surface direction perpendicular thereto. By aligningthe direction of greater shrinkage with the direction of wire travel, itthereby becomes possible to further enhance randomization of the wirepattern in accordance with objectives of the present invention.

It can be appreciated from the foregoing description of one embodimentemployed to fabricate the composite sheet member that various othermethods could be employed with comparable results. More particularly, itis contemplated that a plurality of individual prestressed wire lengthscould be applied under tension to the major surface of a polymer sheetand after being secured at each end to said sheet in the mannerpreviously described then permitted to undergo the same general typeheat shrinkage procedure. It is also contemplated to prestress theresistance wire with a misaligned drawing die when drawing the wire andprovide such prestressed wire under tension during assembly of thecomposite sheet member. Likewise, it is further contemplated thatdifferent equipment than above described could be designed for applyingprestressed resistance wire under tension to one major surface of thepolymer sheet and thereafter automatically carrying out the heatshrinkage operation. It is intended to limit the present invention,therefore, only to the scope of the following claims.

We claim:

1. An apparatus for assembling a thermoplastic polymer sheet having awire pattern partially embedded therein which comprises:

a. support means permitting a thermoplastic sheet to shrink from itsoriginal dimensions when heated to an elevated temperature,

b. tensioning means to apply a pattern of prestressed wire to one majorsurface of the supported polymer sheet so that individual wires lie inclosely spaced parallel relationship with respect to one another,

c. fastening means to secure opposite ends of the wire pattern along thedirection of the wire path to the major surface of the polymer sheet,

d. means to relax the tension upon the individual wires so that saidwires adopt a configuration attributable to the prestress forces whilemaintaining the polymer sheet in physical contact therewith, and

e. heating means which cooperate with said support means to shrink thepolymer sheet so as to have partially embedded therein a plurality ofthe individual wires such that portions of said individual wiresprotrude from said major surface of the polymer sheet. I

2. An apparatus as in claim 1 wherein the support means comprises acollapsible drum which can be reduced in diameter a predeterminedamount.

1. An apparatus for assembling a thermoplastic polymer sheet having awire pattern partially embedded therein which comprises: a. supportmeans permitting a thermoplastic sheet to shrink from its originaldimensions when heated to an elevated temperature, b. tensioning meansto apply a pattern of prestressed wire to one major surface of thesupported polymer sheet so that individual wires lie in closely spacedparallel relationship with respect to one another, c. fastening means tosecure opposite ends of the wire pattern along the direction of the wirepath to the major surface of the polymer sheet, d. means to relax thetension upon the individual wires so that said wires adopt aconfiguration attributable to the prestress forces while maintaining thepolymer sheet in physical contact therewith, and e. heating means whichcooperate with said support means to shrink the polymer sheet so as tohave partially embedded therein a plurality of the individual wires suchthat portions of said individual wires protrude from said major surfaceof the polymer sheet.
 2. An apparatus as in claim 1 wherein the supportmeans comprises a collapsible drum which can be reduced in diameter apredetermined amount.